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WOLF BLITZER, CNN ANCHOR: -- their ferry sank off their -- off the coast of South Korea. Many are high school students and teachers. They were on a class trip. We're going live to Seoul, South Korea.

Also right now, the U.S. Navy search vehicle is back in the water after a technical glitch interrupted its second day of searching for Malaysia Airlines Flight 370. We'll take you live to Perth, Australia.

And right now, tensions are soaring in eastern Ukraine. Pro-Russian militants trying to tighten their grip as Ukrainian forces move in. We'll take you live to one of the towns caught in the middle of the standoff.

Hello, I'm Wolf Blitzer reporting from Washington. We begin off the coast of South Korea where a ferry has capsized with hundreds of high school students aboard. The students were on their way to a resort island for a class trip. At least four people are confirmed dead in the disaster, a figure almost certain to climb higher. A hundred and sixty-four people have been rescued.

Right now, boats, helicopters and divers, they're frantically searching the frigid waters for the nearly 300 people, mostly high school kids who are still missing. This video which CNN cannot authenticate appears to show a scene inside the vessel as it's sinking. It shows people in life jackets and is time stamped with today's date.

Andrew Salmon is joining us now live from Seoul with the very latest. Andrew, families of these students are frantic for information. What is the very latest? What are you hearing?

ANDREW SALMON, CNN CORRESPONDENT: You're absolutely right, Wolf, people are frantic. Adding to the dimension of this tragedy and the early stages of the search and rescue operation, it was reported that a great number of people and all the students had been rescued. But as the day wore on, we discovered that this information was completely incorrect. Actually, the majority of people are still missing and very -- a very large number of the students. I can't give you the exact numbers. The figures we've got, the latest -- I'll give you the good news first.

And the good news is in short supply here, 179 people have apparently been rescued, six people are confirmed dead. And between 277 and 290 are still unaccounted for, still missing. And it looks likely they are trapped in the sunken hulk. Again, the ship, for unknown reasons, had a sudden accident, list very, very heavy, was still afloat for about two hours, giving a good time window for people to get off, then finally capsized, sank by the stern. The last we've seen of her, the ship, the (INAUDIBLE), all that remains is just a section her bow protruding above the water. So, again, to reiterate, there's a large number, 277 to 290 people, the majority of them schoolchildren, young high schoolchildren, possibly trapped under water in this sunk -- sinking hulk.

BLITZER: So, Andrew, basically, what I hear you saying, is at least a little bit of that ferry is still above water, so the hope is that maybe some of these kids and others inside, they got to some space where there's an air pocket or whatever, where they might still be alive. Is that the hope that people are going through right now?

SALMON: That is the hope and I can't honestly tell you, as a layman, how realistic that hope is. We know about 170, 180 elite Navy divers are on the sea. So, you know, cometh the hour, cometh the man. These guys may -- just may be able to somehow get into the hull under water, move inside this dark, cold, freezing labyrinth under the water and reach people trapped in air pockets. But if they do reach these people, how they extricate them from that situation, this is an extraordinary dangerous and demanding operation for these young men. So, hopes are strong, but reality -- your guess is as good as mine.

BLITZER: Yes, and it's now after 2:00 a.m., clearly in the middle of the night over there. But the search operation, the rescue operation is continuing throughout the night, right?

SALMON: The rescue operation has very recently just been resumed. There's -- a U.S. Navy ship is on standby in the area. But there's a huge number of South Korean assets circling the stairwell (ph). If you look at the early pictures, you saw not just coast guard vessels, but even fishing boats going up to the sinking ship, taking people off, you know, at considerable risk to themselves. We've also had some indication of why the casualty toll may be so high. What happened was the ship lifted (ph) very, very suddenly.

So, although it took about two hours to actually capsize and sink, many of the people aboard, according to survivor's accounts, were unable to climb up these very, very steep decks and the water was coming in, the lights had gone out. A nightmare situation. Compounding the problem was an order which came over the P.A. system aboard the ship, telling people to put on your life jackets and stay where you are. As I'm sure you know, in any maritime or naval disaster, the key thing is to get up from below, get top side, get on deck, where at least you can get into the water and possibly be rescued. So, this order for people to stay where they are and not to move is questionable, to say the least.

BLITZER: It certainly is. All right, Andrew, we'll check back with you. Andrew Salmon, he's on the scene for us in Seoul, South Korea.

Let's go to Perth, Australia, right now, in the search zone in the Indian Ocean. That's where an underwater vehicle is looking for any signs of Malaysia Airlines Flight 370. Here are the latest developments. The submersible drone Bluefin 21 resurfaced earlier today because of a technical problem. But it was redeploy and is scanning the depth of the ocean right now. We could soon find out the results of tests of an oil slick spotted by the ship, Ocean Shield. A two-liter sample was taken to Australia for analysis. Standby.

And angry relatives of those on board Flight 370 stormed out of a conference room at a Beijing hotel today. They are so upset about the technical problems with the video conference by Malaysian officials and that's only added to the anguish, the frustration, they've been experiencing now for the past 40 days.

Today's glitch was the second setback for the Bluefin 21 drone. But what does this mean for the overall search effort?

Let's bring in our Correspondent Will Ripley. He's joining us now live from Perth, Australia. Will, have the crews been able to retrieve any data, significant data? Have they learned anything important so far in those two attempts by the Bluefin 21 to go under the water and find something?

WILL RIPLEY, CNN CORRESPONDENT: All the data that's been retrieved so far has shown that there's really nothing of interest in the areas that have been searched. But keep in mind, the Bluefin 21 has had its missions cut short twice now. Dive number one because the depth of the water was too much for this -- for the equipment and its programming so it aborted the mission automatically.

And then, on Wednesday morning, glitch number two. We don't know the nature of the technical glitch. We've been asking that question. Haven't gotten an answer. But we know that the Bluefin had to come back up. They took what data was on there. Didn't find anything. And as far as we know right now, Wolf, the Bluefin 21 is operating normally and perhaps number three will be a charm here to be able to actually complete a full mission.

BLITZER: But, right now, that Bluefin 21 is under water and they're hoping they've fixed the technical glitch, whatever that was. They hoped they reprogrammed it so it can go deeper than the first attempt. So, we have no result on try number three yet, right?

RIPLEY: Yes, because when the Bluefin is down and doing its work, there is no real-time data sharing between the Ocean Shield and the Bluefin 21. They have to wait until the device comes back up before they can download that data from the submersible. And so, -- and then, after that, you know, they go through it. They look at the images. They look at the screen to see if there are any shapes that stand out as potential debris, potential wreckage from an aircraft. So far, what the Bluefin has seen has not indicated anything like that.

BLITZER: The oil from that oil slick, the two liters that have been brought -- I don't know if it's arrived already in Perth, Australia, where chemists, they're taking it to a laboratory to see if it is from the jetliner. What's latest that we know about its location and the analysis, if, in fact, it has already reached some sort of lab?

RIPLEY: As far as we know, it was due to arrive this afternoon in a matter of hours. So, now, here we are in the early morning hours and near the command center, the coordination center here in Perth. As far as we know, the sample is now being analyzed or at least it's at a lab where it will be analyzed.

So, we're told that those results could actually turn around pretty quickly, whether it's oil or some other hydraulic fluid. They're going to try to see if the fluid that was found in the water would be a fluid that you'd find in that Boeing 777 and if it was, in fact, leaking from the surface. So, we could get answers relatively soon on that, Wolf. We'll have to wait and see.

BLITZER: As soon as you get that answer, let us know. Our viewers are, obviously, interested in knowing if, in fact, that oil is from that Malaysia airliner. Will Ripley, thanks very much. Will Ripley is live in Perth.

Let's go live to Ukraine right now where we're seeing more extraordinary and even confusing scenes play out. Take a look at the map. Uprisings are now taking place up and down eastern Ukraine, all about 100 miles or so from where Russian troops, many of them, thousands, have massed on the Russian side of the border. Armed vehicles carrying the Russian flag rolled through at least two eastern Ukrainian towns today. But a number of them apparently are Ukrainians. Ukrainian officials say some of the tanks were seized by local militia.

And, here, dramatic pictures from Donetsk. You can see a local man risking his life to keep armored vehicles from getting any further. This is amateur video, by the way. We can't confirm it but it certainly does look like this man is trying to stop them, first using his hands and then by lying down in front of the vehicle.

Our Senior International Correspondent Nick Paton Walsh is right in the middle of all of this. He's joining us now from eastern Ukraine. So, what have you been seeing today, Nick? Because there have been some very tense, very dramatic moments. NICK PATON WALSH, CNN SENIOR INTERNATIONAL CORRESPONDENT: An extraordinary day. The Ukrainian army, it seems, moving into Kramatorsk, one of the towns to the north of where I'm standing now in some number (ph). They're running into locals who gave up resistance, blocked their path. And then, it seems, pro-Russian militants moved in and took those armored vehicles away from the Ukrainian soldiers who were driving them.

They then took them to Slovensk. That's where we started seeing pictures of the Russian flag and the Donetsk separatist flag on these armored vehicles. And then, paraded them in the center of town for quite some time. Those Ukrainian soldiers themselves, we understand from talking to the self-declared mayor of Slovensk, were, in fact, not voluntarily surrendering themselves, did this under force, and were then taken inside Slovensk for lunch (ph).

But there seems to be a pattern emerging here really. Very little sign of effective Ukrainian military presence on the ground. We've seen them on the skies, helicopters and jets a lot of the day, and still at the airfield near Kramatorsk.

But we actually went to another village near Kramatorsk or Pachokina (ph) where we saw a quite remarkable scene. It appears that a column of Ukrainian armor -- and these aren't anybody. These are a 25th paratrooper division, considered to be some of the best troops, in fact, that Ukraine should even have, came into this village. Now, we don't see this ourselves, but we heard from a number of residents, claimed that they had shot in the air as they came through. And even they may have damaged a car, at some point as they traveled. That caused significant local anger.

And then, the -- many people in that village came out and flooded around the vehicles, making it impossible for them to move. And there were lengthy discussions, at that point. A local police chief came down, a veteran from the soviet war in Afghanistan, all together trying to work this out.

And then, eventually, a decision was made between what's calling itself now, the Donetsk people's army. And that's pretty much sort of the less prepared part of the pro-Russian militants we've seen here. They had a discussion which they agreed the Ukrainian troops would take the kind of firing blocks out of their AK-47 assault rifles. We saw them put them all into a large plastic bag, hand them over, and would then be allowed to leave.

We didn't see, actually, the column finally depart but the atmosphere had calmed down somewhat. But it is just quite remarkable to see what should be the Ukrainian shock troops, so to speak, run into a village, meet such local resistance and then, effectively, give up -- Wolf.

BLITZER: Yes, because, as you say -- I was watching you earlier today on CNN's "NEW DAY" and you were in front of one of those Ukrainian tanks and there were a lot of people on top of the tank. But you say it was peacefully handed over from Ukrainian troops, or at least one Ukrainian soldier, to these pro-Russian demonstrators, if you will. Is that what I was seeing?

WALSH: Well, what you saw on "NEW DAY," those images of pro-Russian militants on top of an armored vehicles, those guys, they're not really peaceful in many ways. They are very well trained. They have top-end weaponry. They're very disciplined. And they're obviously running the show here. They even told the self-declared mayor, at one point, stop talking and get inside the building they were protecting. So, there's definitely a very well-organized element here which Washington and NATO and most western capitalists say, it's basically Russian organized or Russian led here.

But it does appear that the village we were at, in Pachokina, people surrounding those armored vehicles who, eventually, it seems, made a deal that potentially would let them leave. They were, for the most part, unless I missed something, peaceful civilians. They're angry at the Ukrainian military presence. They've angry at the government in Kiev who they say they don't trust. A little misinformation, too, about the Kiev government's intensions though. But certainly, when it comes to the armored personnel carriers paraded in Slovensk, where the pictures you mentioned earlier on, they seemed -- were confronted, it seems, by pro-Russian militants and by peaceful residents, too. And then, at that point, the Ukrainian military seems to have made the decision, those guys traveling in those armored vehicles, to hand them over or at least give up control of them.

We didn't see many of these Ukrainian soldiers. I saw one, in fact, come out under armed escort, go to his own vehicle and take out some of his stuff from inside it and then go away. But then, those pro- Russian militants, very well equipped, pretty well trained, very disciplined and absolutely running things, took the vehicle, drove off -- Wolf.

BLITZER: Yes, and U.S. officials insist many of them are actually Russian citizens themselves, not Ukrainian citizens. But that is disputed by the Russians. All right, stand by, we're going to get back to you. Nick Paton Walsh, on the scene for us in eastern Ukraine.

Another major story we're following today, the kidnapping of more than 100 school girls by Islamic militants in Nigeria. Even though the school had armed guards, members of the militant group, Boko Haram, were able to get the students onto vehicles and flee into the bush. We're going to have much more on the efforts to rescue these girls. That's coming up later. Our own Christiane Amanpour is working this story. She'll join us live.

Also ahead, the Bluefin 21 makes a deep dive in search of the missing Malaysia Airlines plane. But what does the latest technical glitch mean for this entire search operation? Our experts, they're standing by to weigh in.

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BLITZER: The underwater vessel searching for Malaysia Airlines Flight 370 is on its latest deep dive in the Indian Ocean right now. A technical glitch caused the Bluefin-21 to return to the surface, but it was then redeployed and is continuing its search now. Let's bring in our experts. Peter Goelz is a CNN aviation analyst, former NTSB managing director. Tom Fuentes is our law enforcement analyst, a former FBI assistant director.

All right, so, Peter, first time they didn't program it right, the Bluefin-21. It couldn't go as deep as it should go. Automatically came back up. Second time there's some unknown technical problem that's forced it to come back up. They think they've fixed it. It's now down there. How much of a problem is there with this Bluefin-21?

PETER GOELZ, CNN AVIATION ANALYST: This is a complex piece of equipment in a very challenging environment. Don't think it's, you know, a big deal yet. I mean they need to get it right. It's going to take a few shots at doing it. Let's see how it finishes out today's assignment. But this is very difficult.

BLITZER: The air search is still continuing right now. They're still looking on the surface of the Indian Ocean for something. So far, 40 days, it's now day 40, they haven't found anything. At what point should they just give up the air search and focus in where they heard that pinging sonar, that pinging device go off for two hours and 15 minutes and five and six minutes, four pings from this general area? What point do they just focus under water?

TOM FUENTES, CNN LAW ENFORCEMENT ANALYST: I would think maybe now's the time. I mean they haven't found anything ever, much less, you know, the last few days. And, you know, the amount of type and bad weather and all of the other factors of not being able to find anything after 40 days, it might be time now.

BLITZER: Sometimes you hear stories, tsunamis, weeks or months later stuff shows up on shore because it's moved across the Pacific or whatever. You expect anything like that could happen in this particular occasion?

GOELZ: Yes, I agree with Tom, I think the time is right. Crews could be tired. But, yes, I do think at some point something's going to show up. But the time now is to focus under water.

BLITZER: You have any confidence at all that this oil slick, or whatever they found, and it's now being examined, we should probably know later today whether or not it is from the plane or not from the plane, you suspect it could be from the plane? How serious of a possibility do you think that is?

FUENTES: I don't know. You know, listening to the experts, it sounds like that's a long time for anything like that to sit on the surface and still, you know, be together, not having been disbursed or sunk or dissolved or some other factor. So, to me, it sounds unusual that 40 days later you'd have, again, an oil slick that, you know, collected together to be able to have it from the airplane.

BLITZER: You agree?

GOELZ: Yes, I think it's a long shot.

BLITZER: It's certainly a long shot.

Let's talk a little bit about the families. Once again, they're so frustrated, they're angry. They were on a conference call with Malaysia and Beijing and, obviously, there was serious technical problems. You dealt with families on a lot of these kinds of investigations. They are still so angry and so many of them are refusing to believe that this search is really being conducted in the right place. They want to believe, and many of them probably still believe, their loved ones are alive.

GOELZ: It is a very challenging situation. The issue is, is they've also received minimal compensation so far. Just a single check. I think they've got to figure out how to give the families some degree of financial compensation that doesn't replace -- doesn't prevent them from suing but, you know, how unfair is it that they're sitting there 40 days afterwards with sometimes their breadwinners gone, what are they doing? BLITZER: Short of finding some wreckage from the plane, I don't think there's any way they're going to convince a lot of these families that their loved ones really are gone.

FUENTES: No, I think that's true. I think they're convinced until they see something, some piece of evidence, they're not going to be convinced.

BLITZER: And if they're on social media, they see all these wild tales of where this plane really is, and many of them probably start believing it, not because they think it's true, they just want to have hope that their loved ones are alive.

GOELZ: Until we showed the family members actual tapes of the TWA wreckage and exactly how devastating that was, we had the same issues at TWA.

BLITZER: Peter, Tom, guy, thanks very much.

Still ahead, another school in Nigeria comes under attack from Islamic militants. This time, more than 100 girls are kidnapped. How could this happen in this day and age. We'll have the latest on the efforts to rescue them. That's coming up.

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BLITZER: We want to turn our attention to a developing story out of Nigeria right now, where the country's military is desperately hunting for more than 100 girls who were kidnapped from their school dormitories and taken into the bush on trucks and buses. The Islamic group Boko Haram is believed to be behind the attack. They've carried out similar assaults against Nigerian schools in their attempt to create a strict Islamic state. Our chief international correspondent, Christiane Amanpour, is joining us from New York right now.

Christiane, Boko Haram has been especially ruthless towards these children. What's the greatest fear right now if these girls aren't rescued quickly?

CHRISTIANE AMANPOUR, CNN CHIEF INTERNATIONAL CORRESPONDENT: Well, a huge fear. And the Nigerian government has put a huge military detail on trying to find them as they continue to be missing. And what happens, according to a lot of the experts who have been tracking these kinds of abductions, is that in Nigeria particularly, these girls are often then sold into the sex slave industry or some kids are trafficked around and become child soldiers. And this epidemic and this crisis of child abductions is battering Nigeria and has been doing so since at least 2010. And Boko Haram is becoming even more active than it was then.

For instance, at the beginning -- since the beginning of this year, something like 100 -- 1,500 people have been killed by Boko Haram in Nigeria, compared with about 3,000 over the previous three years. So it's a situation that's getting worse.

And even though Nigeria's president, and I've questioned him many times on this, says that they're doing all they can to try to stop it and to neutralize Boko Haram, the military tactics are blamed for actually stoking the flames of this crisis because many critic say that when the military goes in to try to either find abducted children or to tamp down these militant attacks, they go out and sort of indiscriminately attack villages and burn homes and kill people and that, many complain, that the situation gets worse because of it, Wolf.

BLITZER: Well, from this perspective of Boko Haram, this group, what does kidnapping young girls and selling them off as sex slaves, if you will, what does that have to do with creating a strict Islamic state?

AMANPOUR: Well, you think that those would be a contradiction in terms. And, of course, they are. Well, first of all, the word "Boko Haram" means "western education is forbidden." It's basically against western education. So they target students, you know, saying that this matches their mission statement, so to speak.

But then they want money. So this is a very, very lucrative industry, as you know, around the world. Over $1 billion a year in the sex slave and sex trafficking, Asia's organization (ph), and that so -- is a huge source of finance for these people as well.

But beyond that, you know, they're just trying to attack the fabric of those kinds of communities and put as much pressure on the Nigerian government as they can. For instance, the government used to say Boko Haram's activities are only confined to that part of the northeast of the country where they started. But, in fact, in this last week alone, 70 people were killed in a bomb attack in the capital Abuja and more people have been killed in the intervening days in other attack. So they're spreading their very destructive capabilities as well.

BLITZER: What a horrible, horrible story that is. Christiane, thanks very much. Christiane Amanpour reporting.

Just ahead, technology is leading the way in the search for Flight 370, but why haven't all those sophisticated gadgets found the plane?

And tensions are heightened in Ukraine right now. Armed pro-Russian separatists are taking over key buildings in eastern cities. Can this be stopped?